(1) Field of the Invention
This invention relates, in general, to a photofinishing operation. More particularly, it relates to a system and apparatus for reducing the amount of fresh water used in the processing of photographic film and to the reduction in energy costs saved by not having to heat that amount of water. Further, the invention relates to apparatus means and a process for extracting silver from photofinishing wash water solutions on a recirculation basis and for controlling biological growth in the recirculated wash waters.
(2) Description of the Prior Art
In the processing of photographic films and papers, there are three processing solutions -- the developer, the fix or hypo, and the wash bath. The first develops the image and no silver is removed from the film or paper. The fix or thiosulfate bath converts the unexposed silver halides to silver metal and dissolves the exposed areas into the fix solution. The film or paper is then transported (most often in automatic film processors) via rollers to the wash bath. The wash bath functions to "wash-off" the residual silver thiosulfate and thiosulfate remaining on the film or paper surface.
Various silver salts employed in the manufacture of photographic paper and film go into solution in the various aqueous fix or hypo solutions. These spent processing solutions contain a relatively large concentration of silver and are, in general, processed to remove as much of the silver therefrom as possible. The need to remove an even greater amount of silver from these spent photo fix solutions, due to environmental regulations, among other considerations, has prompted considerable research and development effort, to provide more effective recovery systems. One such an effort is disclosed in U.S. Pat. No. 4,800,005, which issued to me on Jan. 24, 1989.
Although the novel electrolytic unit disclosed in U.S. Pat. No. 4,800,005 is quite successful in the recovery of silver from a spent hypo solution, such a system and apparatus does not work well in the recovery of silver from wash or rinse water effluent from the photofinishing operations. This wash water, like the fix solution, contains dissolved thiosulfate ions, and ions of silver thiosulfate. One reason for this ineffective removal is the relatively low or dilute concentration of silver thiosulfate ions in those solutions compared, for example, to the concentration of silver thiosulfate in the spent fix solutions.
Photoprocessing of film can use several hundred or thousand gallons of fresh, heated (to about 72 degrees F.) water per day. With presently, and ever increasingly expensive water and sewer rates, a lesser consumption of fresh water could mean a real and substantial dollar savings to a film processor. Further, additional savings could be realized through less energy costs as a lesser amount of water is heated.
Until the somewhat more recent past, these wash water solutions were commonly discharged into a connected sewer system, or otherwise to the environment, e.g., into a stream. In cases where the film processor might be on a septic system, the wash water solutions are collected in suitable containers and later hauled away for disposal. More recently, however, there has been an ever increasing concern about the discharge of such hazardous waste material, e.g. waste containing heavy metals, as does the photofinishing wash water, into the environment, due to various local, state and federal regulations. Further, the Environmental Protection Agency ("EPA") has recently found that silver when linked with copper (found in almost all water discharges) forms a compound very hazardous to marine life. This copper/silver bonding has resulted in California and Nevada banning all silver discharges into Lake Tahoe. Of concern also in some areas of the country, in addition to environmental regulations, water consumption is actually being restricted. Accordingly, there is a real need, particularly in the wash water solutions in photo processing operations, to reduce the consumption of fresh or city water.
Heretofore, others have been concerned with at least certain of these various problems in photofinishing operations. Nevertheless, the primary concern has been mostly in reducing the amount of silver in the wash water solutions. This is so that such solutions would meet the various regulations for disposal of hazardous waste and such could then be discharged directly to the environment.
The recovery of silver by ion exchange has not long been practiced. Its application to the photographic industry has been prompted in relatively recent years, primarily due to three factors, i.e., economic situations have made it profitable for laboratories to recover silver from dilute wash water solutions, conservation of a valuable natural resource, i.e., water; and compliance with increasingly stringent discharge effluent regulations by various government bodies, as earlier alluded to, e.g. the EPA and regional waste treatment plants. Even so, however, little attention has been given to such problems encountered by the relatively small scale users in the whole of the photographic sector, e.g., in particular, in the medical x-rays and graphic arts (e.g., newspapers and printers) areas, relative to somewhat larger users of even higher volumes of water in the processing of photographic film, e.g., the processing of black-and-white and color print film and color slide film.
Others prior to the invention disclosed herein have considered the recycling or recirculation of the wash water solutions from photofinishing operations. In one such an operation, wash water is merely recycled to the photofinishing operations for use again without any concern about the recovery of silver. Although there is consumed less fresh water in such a system and there is a savings in energy costs as well, the recycling of untreated wash water in such a manner to the photofinishing operation is attendant with certain problems. One particular problem involves the build-up of bacteria slimes in the collection or holding tank for the wash water which is to be recycled. Even of more concern is the build-up of bacteria slimes in the photofinishing apparatus. This necessitates shut-down of the processing and cleaning the apparatus involved.
A solution is now classified as hazardous waste when it contains over 5 parts per million ("ppm") silver. When photo wash waters are not recycled or recirculated as indicated earlier, they, in general, most often contain less than 2.0 ppm silver, which is just within the discharge limits established to date by many municipal waste treatment plants. Nevertheless, an untreated recycled wash water solution, i.e., one wherein there is no concern about silver recovery, may contain as much as 200-3,000 ppm silver. As a result, there is much reluctance on the part of photofinishers merely to purchase a recirculation system because the water and heat savings are offset by hazardous waste removal expenses and other regulatory requirements.
In another recirculation system of which I am aware, that system does involve the recovery of silver. Nevertheless, in this system the wash water is recycled until such time that the concentration of silver is sufficient to make it practical and economical for recovery. The silver is then recovered from any such silver concentrated wash water that is to be discharged from the system to waste, to meet the hazardous waste requirements established by any federal, state and local requirements. These systems employ either steel wool or ion exchange resins to remove the silver before discharge to the sewer. There are several problems peculiar to such a recirculation and silver recovery system. For example, (1) Large quantities of steel wool or ion exchange resins are needed to treat a "surge" discharge of the recycled wash water; (2) This effluent is often recirculated a week or more, thus it can contain large concentrations of thiosulfate and silver thiosulfate ions. Ion exchange resins, in particular, have difficulty holding on to the silver thiosulfate ions when so many other free thiosulfate ions are present. Thus many milligrams of silver could be inadvertently and illegally released to the sewer; and (3) Between the small ion exchange resin beads is space for the liquid (wash water) to flow. With the presence of low level thiosulfate, warmth, and darkness, biological growth often explodes exponentially--resulting in clogged resin columns and resin too fouled to recover silver.
Another photo wash water circulation system of which I am aware involves the recovery of silver by means of ion exchange. Nevertheless, this system requires on-site, periodic regeneration of the ion exchange resins to prepare the sites on the ion-exchange resin for additional silver recovery. Thus, with use of such a system one must also purchase a regeneration unit. Although such units are built for use by so-called "mini-labs," there are certain disadvantages in their use. The regenerator, though relatively small and portable, nevertheless takes up some floor space, space that is valuable and not always available in a small scale photofinishing operation. Moreover, such regeneration units commonly involve the use of sulfuric acid which is not only of some concern in handling and use, because such is a strong acid and very corrosive, but also can be quite odoriferous. Also, these systems must be "backflushed" to wash out the build-up of biogrowth and impurities found in the wash waters. Backwashing often is a daily practice resulting in the shut down of the processors, thus stopping film processing. Further, when backwashing or regeneration must be done, there is the high probability of washing silver down the drain in the process. This can result in illegally dumping silver into the waste stream or environment.
In a further system now being used, and involving silver recovery as well as recirculation of wash water, the wash water rinses or solutions are collected in a tank and then passed through ion exchange units for recovering the silver. This system involves periodic backwashing of the bed of ion exchange resin to remove emulsion gelatin and prevent clogging. This is accomplished by the reverse flow of city water through the resin containing bottles or tanks taken out of service momentarily for this purpose while another silver extraction ion resin column is substituted in its place. In addition to such periodic backwashing of the ion exchange column, a column loaded with silver is removed (with substitution of a regenerated resin column in its place) from the system and regenerated. Silver removed from the ion exchange resin is then recovered from the regeneration solution electrolytically. Following the removal of silver, the wash water solution effluent is brominated to prevent growth of bacterial slime or algae and to oxidize any remaining fix. It then is passed to a distribution tank whereat city make-up water will be added to the wash water solution if processor demand should exceed recycling capacity. Water from the distribution tank can be recycled to any of the originating washes following, according to the manufacturer, a small increase in temperature and approximately 10% dilution with fresh water to prevent a build-up of chemical salts.
Such a system suffers many of the disadvantages described earlier, e.g. surge discharges, large build-up of thiosulfate ions from too much recirculation, clogged resin columns needing back flushing, and biogrowth. Furthermore, it has been discovered that chloride or bromide tablets which some companies sell to control biogrowth are ineffective because the acetic acid found in fix solutions has been found to neutralize them.
A further disadvantage with the just mentioned system is its cost. This system is easily 2-3 times the size of the film processor. It requires in some states such as Massachusetts and Rhode Island that the operator become licensed as a waste treatment plant operator.
As to biogrowth problems, ultraviolet light has also proved to be ineffective, apparently, because the UV light can only penetrate a very small surface and the water must be flowing past it 24 hours a day. Further, ultraviolet light glass tubes which come in contact with the wash water quickly become plated with silver halide as such reacts with the exposure to the UV light.
Ozone, a strong oxidizer, was also found to be ineffective on biogrowth. The ozone generated not only did not control growth but too much ozone in a darkroom can make people ill. Moreover, the ozone caused the wash water to turn ink black. Once the ozone was turned off, the biological growth increased rapidly.
Thus, there is still a need by the photoprocessor for a system that is not only economical in cost but one which is efficient in silver recovery and which reduces water consumption significantly with no hazardous waste by-product as a consequence. And there is a need that such a system operate to inhibit biogrowth not only in the wash water collection tank but throughout the system. This need is particularly great by the small scale operator.
Photoprocessing is practiced by graphic arts operations--printers, newspapers, typesetters; x-ray operators--medical x-ray, industrial x-ray; photographers--photofinishing, motion pictures, aerial, testing, etc. and microfilming. All these areas of photoprocessing are now subject to low silver discharge limits. Thus, in some geographical areas a small scale operator may be the local newspaper. In other areas such as Long Island, N.Y. or Cape Cod, Mass., the local dentist or chiropractor may be the photoprocessor that must treat such waste.
The above needs for treatment of photoprocessing wash water can arise in a number of different ways, e.g., as a result of:
(1) locally mandated regulations and restrictions on water usage (e.g., California, Florida, and Long Island, N.Y.); PA1 (2) a photoprocessor's desire or need to control water related costs, e.g., the rising use and discharge fees, and energy costs relating to the heating of wash water; PA1 (3) a photoprocessor's need to comply with environmental discharge regulations, in some cases, in concentrations as low as parts per billion; and PA1 (4) a photoprocessor's desire or need to control waste disposal costs--if the waste water is hauled for disposal or sent out for post treatment the resulting expense directly impacts competitiveness and profits.
Also there is need by the photographic film manufacturers to demonstrate to their small and medium size customers that film based technology is environmentally and economically cost competitive with the newly emerging electronic publishing.